1. Field of the Invention
The present invention generally relates to a containment vessel system and method for handling (e.g., sorting and/or shipping) of toxic wastes, solid radioactive wastes such as plutonium. The invention relates more particularly, to a tracking system and method for audits based on a low frequency electronic radio tag placed within the containment vessel. The present invention relates to what might be called a smart containment vessel for storage of solid hazardous waste materials using the radio tag's memory to store the history and full pedigree of the waste contained in the vessel. More particularly, the present invention is directed to containers prepared from cementitious materials capable of long-term safe storage of certain highly toxic and nuclear waste materials with an embedded low-frequency radio tag that can provide accurate audits and pedigrees of weapons-grade nuclear waste for many hundreds of years.
2. Description of the Related Art
In recent years, the public has become more sensitive to the environment and the effect of hazardous and toxic waste materials on the environmental ecosystem. Nuclear waste materials are some of the most dangerous toxic wastes because they can remain radioactive for extremely long periods of time. There is, therefore, a serious need for effective long-term storage containers for nuclear and other hazardous waste materials.
Much of the nuclear waste materials which need to be disposed of include refuse from nuclear weapons plants, civilian power plants, and medical industry sources. Unlike spent fuel rods which decay by emitting high level gamma radiation, the plutonium waste from weapons plants decays by alpha radiation, which is unable to penetrate paper or clothing. An alpha particle is equivalent to a helium nucleus, having two protons and two neutrons. As a result, the plutonium waste materials from weapons plants may be handled without protective clothing and pose no danger, as long as they remain sealed. Nevertheless, plutonium is extremely toxic and very long-lived. In addition, it is estimated that sixty percent (60%) of the plutonium-contaminated waste from weapons plants is also tainted with hazardous chemicals such as industrial solvents.
Gloves, shoes, uniforms, tools, floor sweepings, and sludge contaminated with radioactive materials while manufacturing nuclear warheads are typically placed in 55-gallon steel drums for containment as hazardous waste items. The Waste Isolation Pilot Project (“WIPP”) site near Carlsbad, N.M., is one possible disposal site for such waste materials. The WIPP site was excavated in a massive underground salt formation. Underground salt formations, such as the WIPP site, are considered as possible permanent clear waste disposal sites because of the long-term stability of the underground formation and because salt has a low water permeability.
In one possible disposal plan using underground disposal sites for low-level nuclear waste materials, the underground rooms are filled with the waste containers and back-filled with a grout material to fill as much empty space as possible. During the first 100 years, the underground storage rooms would typically collapse and crush the waste containers.
One problem with conventional 55 gallon steel drums is that eventually, the drums will be crushed when the storage room collapses; however, the presence of empty spaces permits ground water to seep into the cavities which can cause corrosion of the steel drums and decomposition of organic waste materials. Since the disposal site is not completely sealed until the underground storage room collapses and fills all void spaces, rapid collapse of the storage room is desirable so that the disposal site is sealed quickly. Another disadvantage of conventional 55-gallon steel drums is that they are potentially capable of undergoing corrosion which would produce gases, especially H2.
An ideal solid hazardous waste container should satisfy some of the following desired characteristics:                (1) The container should be made of a nonmetal or other material which intrinsically does not corrode and produce gases;        (2) The container should be inexpensive;        (3) The container should be impermeable to water and, if water does penetrate the container, it should act as an H2O “getter”, i.e., it should combine with water to form an insoluble solid;        (4) The container should have CO2 “getter” characteristics, i.e., it should react with CO2 to form a solid; and        (5) The container should be of a material which expands if, for any reason, an aqueous solution does breach the impermeable outer layer. Expansion of the material on contact with water seals and fills any cracks in the container wall, and also fills any space between the storage container and the walls of the salt mine which collapse around the container. Such containers have been disclosed and described in U.S. Pat. No. 5,100,586 (issued to Jennings, et al. on Mar. 31, 1992), and U.S. Pat. No. 5,543,186 (issued to Andersen, et al. on Aug. 6, 1996). A sixth requirement is:        (6) The container should have a tamper-proof system capable of providing adequate information on the container contents and history. Such a system should be able to be read remotely without opening the container, and ideally while the container is buried. For example, it would be helpful to have a secure electronic pedigree that can be tracked and traced for a minimum of 50 years—preferably remotely by using a radio tag or other electronic system.        
An additional major problem is that once waste materials have been placed inside the drums or other containment vessels, they often must be tracked and traced with a strong audit trail from the site where the waste material is placed inside the drum. This is particularly true for weapons-grade nuclear waste (e.g. plutonium) that often is processed in plants in Europe or at other distant locations. This information about the vessel's history, its full contents, chain of passage (COP), and proof of delivery (POD) must be stored and made available to prove that weapons-grade waste materials have not been diverted and the nuclear waste stored in containment vessels is fully intact. One may refer to this as the “Container Pedigree”.
Attempts to use RF-tags or radio tags that use frequencies over 1 MHz attached to the outside of the container as an ID, have proven unreliable for several reasons. In the case of 55 gallon drum containers, the metal can lead to reflections. In the case of the non-metal cementitious containers, the cement itself can block and absorb radio waves, particularly if the outside surface becomes wet, or as is often the case, is surrounded by damp soil.
Most of the commercial RF-tags are transponder devices that receive power from a carrier signal. These have no batteries and are known as “passive tags”. Passive tags have the advantage of no battery, but the disadvantage that they only provide for a weak return signal that is not capable of working reliably in any harsh environment since the carrier power transfer drops off very rapidly with distance. “Active tags”, on the other hand, use batteries that make the tag work as an amplified transponder. However because they use high frequencies they have a typical battery life of only a few years. In addition, if they work at frequencies above 1 MHz, active RF-tags will also have difficulty in harsh environments comprising steel or earth (just as would the passive tags), especially earth with moisture in the soil.
Moreover, in most cases the requirement for any data storage for the container pedigree will be a minimum of 50 years up to 200 years and the information must be read from great distances, (30 feet or more), from the surface and through a thickness of many feet of salt, sand, and soil, since the containers will often be buried underground.
An additional problem with conventional active and passive radio tags, (RF-tags or “RFID” tags), is that they must be attached to the outside of the waste container so they have a major disadvantage in that they may be removed and/or easily altered. However, if instead they were placed inside the waste container, their signal would be blocked by the intervening steel drum and soil, and thus it would be impossible to read the information from the RF-tag.
Finally, most of the active and passive radio tags may have a fixed ID that is programmed at the factory. This requires an external database containing that ID together with corresponding information associated with the vessel. The cost of maintaining a remote, secure, reliable, independent database for the container's pedigree based on a fixed ID's information, especially for hundreds of years, is prohibitively difficult.